This invention is specifically concerned with improved titanium disulfide cathode electrodes, which are particularly useful in electrochemical cells. It is particularly intended to provide electrodes for electrochemical cells of the type including an oxidizable active anode metal and a non-aqueous alkali metal salt-organic solvent electrolyte solution. Preferably, the electrochemical cell will be a rechargeable battery. A preferred battery for using the improved cathode electrodes of the invention is one having a lithium anode and a liquid electrolyte of LiAsF.sub.6 dissolved in a solvent such as 2-methyltetrahydrofuran.
Titanium disulfide has previously been prepared by at least three methods for electrochemical cell usage. In one method, titanium trisulfide is heated to a temperature at which it disproportionates to titanium disulfide and sulfur. Another procedure reacts titanium tetrachloride with hydrogen sulfide to form titanium disulfide. Unfortunately, such titanium disulfide usually contains substantial amounts of chlorine which is undesirable in many instances. Titanium disulfide has also been prepared by directly reacting titanium metal with elemental sulfur at temperatures in excess of 600.degree. C. An improved procedure of this latter technique involves heating particulate metallic titanium to a reaction temperature between about 475.degree. C. and 600.degree. C. and contacting the heated titanium with an atmosphere having a sulfur partial pressure at the reaction temperature. The conditions are maintained for a period of time sufficient to ensure substantially complete reaction between the titanium and the sulfur.
These procedures provide particulate titanium disulfide which must then be formed into an electrode body if it is to be used as a cathode electrode. In the prior art, such bodies have been consistently formed by mixing the particulate titanium disulfide with inert binders such as Teflon, following which it is pressed and heated. Carbon is also ordinarily included in such electrodes bodies.
Due to the vagaries of the compositions of Teflon, carbon and the various solvents required to form a suitable binder, such electrodes can be of non-reproducible composition. Also, the preparation process involves a complicated multi-step procedure.
It is the primary object of this invention to provide porous, rigid titanium disulfide cathode electrodes which are devoid of binders and other additives, except for incidental impurities.
It is another object of this invention to provide a more simplified preparation procedure for making such electrodes.
The improved electrodes of the invention are of uniform composition and exhibit enhanced cycling characteristics in re-chargeable batteries. This allows the batteries to be charged and discharged at higher rates than has been possible with cells incorporating prior art titanium disulfide cathode electrodes.